Construction of sealing ends for high tension electric cables



Feb. 9, 1960 P. G PRIAROGGIA CONSTRUCTION OF SEALING ENDS FOR HIGHTENSION ELECTRIC CABLES Filed June 5, 1956 x xm/ /M/M/// Inventor P I00% oh ROG A LO ZZANA United States Patent CONSTRUCTION OF SEALING ENDSFOR HIGH TENSION ELECTRIC CABLES Paolo Gazzana Priaroggia, Milan, Italy,assignor to Pirelli Societa per Azioni, Milan, Italy Application June 5,1956, Serial No. 589,437 Claims priority, application Italy July 8, 1955Claims. (Cl. 174-73) This application is a continuation-in-part of mycopending application Serial No. 424,729 filed .April 21, 1954.

This invention relates to an improvement in the construction of thesealing ends for high tension electric cables.

It is known that the insulation of the sealing ends of high tensionelectric cables may be built up by hand, at the place of installation,by wrapping onto the cable core (or insulated conductor) insulatingtapes or sheets of insulating paper, or directly inserting onto the endof the cable core one or more prefabricated paper tubes. There is thusobtained an insulating sleeve which is then completed by the applicationof what is known in the cable art as field shields, which may beelectrodes or screens metallically connected to ground or to the cableconductor as the case may be. The unit is then surrounded by aninsulating covering of porcelain or the like.

In the conventional technological practice, the ends of cables to besealed may have to be in various positions as required by dimensions orother special requirements. For instance, in the case of direct entry ofa high tension cable into a transformer, it may be desirable to installan overturned terminal or bushing. In such a structure, the insulatingpaper tubes, owing to their own weight, have a tendency to slidedownwardly, and therefore impair the structure of the insulating sleeve.Moreover, if the external insulator housing is conical, the papertubular insulation, moving downwardly, dangerously approaches the innersurface of the outer insulating housing and may impede the free passageof the oil or of the gas where this is needed.

When the outer insulator housing is of a decidedly conical shape thelower end of the applied paper tube must be tapered. This end happens tobe in a zone which is not screened but is electrically stressed andtherefore presents certain problems.

It is one of the objects of the present invention to provide means forsupporting the applied insulating sleeve against downward movement,particularly in the case of an overturned sealing end wherein the outerinsulator housing is of an approximately conical shape. In accordancewith the preferred embodiment of the present invention, the support forthe sleeve is in the shape of a truncated cone. It may be in the form ofa single piece or, for easier assembly, of several pieces which togetherform a single cone and are bound together. The truncated supporting coneis, in some cases, perforated in order to allow the free access ofinsulating fluid to and from the sleeve that surrounds the cable core.

It is a further object of the present invention to provide a highvoltage cable sealing end wherein the support above mentioned is ofinsulating material having high dielectric 2,924,641 Patented Feb. -9,1960 for the support is a casting of synthetic resins, preferably of theethoxylinic type. Other suitable materials are bakelized cardboard, orhigh dielectric strength porcelain or glass.

The attainment of the above and further objects of the present inventionwill be apparent from the following specification taken in conjunctionwith the accompanying drawings forming a part thereof.

In the drawings:

Fig. 1 is a longitudinal sectional view through a cable sealing endembodying the present invention; and

Fig. 2 is a similar sectional view showing a modified form of sleevesupport in the cable sealing end;

Fig. 3 is a front view', in half section, of a modified form oftruncated cone for supporting the insulating sleeve;'and

'Fig. 4 is a bottom plan view of the structure thereof.

In the drawings like reference numerals designate like parts throughout.

Fig. 1 shows the sealing end of a high voltage cable wherein a cablecore 1 of a high voltage oil-filled or gas filled cable has direct entryinto a transformer. In this case there is installed in the transformeran overturned terminal. The cable core 1 has a paper tube 2 in the formof an insulating sleeve applied thereto at the sealing end thereof, asis conventional, which then extends into an external insulator 3 ofporcelain, which external insulator is of the general shape of atruncated cone mounted in inverse position to extend downwardly into atransformer housing T. The external porcelain insulator 3 is filled withinsulating oil or gas. The lower end of the paper tube or tubes 2 istapered or pencilled downwardly and inwardly from a maximum outerdiameter of the paper tube to approximately the diameter of the cablecore 1. The sleeve 2 is supported by a truncated cone 4 the lower end ofwhich may rest on a sleeve 10 of the same material as the supportingcone 4, and which is in turn supported by a metallic threaded ring 7which is screwed at 9 on a ferrule 8 that is compressed or otherwiseelectrically and mechanically connected over the end of the cable coreconductor. The supporting cone 4 is preferably made of ethoxylinicresins with suitable hardening agents known in the trade under thetrademark Araldit, to which may have been previously added inorganicexcipients such as powdered quartz, kaolin, or the like. If desired, theethoxylinic resins with the hardening agents added, but devoid ofinorganic fillers, may be used. These resins may be used to impregnateunder vacuum (inside a mold) an insulating porous structure of paper,fiberglass, silk, cotton, asbestos, or the like, which is of the shapeof the insulating supporting cone 4 and which within the mold acts as askeleton for producing the support 4, and which structure or skeleton isultimately itself embedded in the casting resin. The composition of thesupport 4 may be any of the compositions described in my pendingapplications Serial Nos. 550,741 or 424,729, and the method of makingthe same may be that described in my pending application Serial No.550,741. The composition is free of voids and has a high tenacity forobjects that may be embedded therein.

The support 4 may, optionally, be perforated as indicated at 4a, so asto allow the fiow of insulating oil or gas therethrough between thecable core and the housing 3.

The support 4 of Fig. 1 may constitute a single casting or it maycomprise a series of separate members which together form the shapeillustrated and which may be held together by a binding of insulation.

At its upper end the paper tube 2 is of a bell shape and is covered witha winding 13 of metallic wire that is electrically connected to thecable sheath. There is also provided a metallic end closure or bell 14that is conventionally sealed with the cable sheath 15.

Fig: 2 shows another embodiment of the present invention. In thisconstruction the cone 4 corresponds to the cone 4 previously describedand may be of the same construction previously described. The sealingend of the high tension cable isprovided with a stress control member 5that is electrically connected to the cable conductor. The stresscontrol member comprises a dielectric mass in which a ring 6 of metal orother conducting material is embedded by casting the dielectric massaround the ring 6. The composition of the dielectric mass and of thecone 4 is the same as that of the cone 4 and the sleeve 19 previouslydescribed. The stress mating grooves 31 formed in the three coneportions.

The three portions 25, 26 and 27 held together by the trol member 5 ofFig. 2 a monolithic unit having a control electrode may be of thestructure and composition shown in my pending application Serial No.550,741 or application Serial No. 424,729, to which reference is herebymade. The lower end of the insulating sleeve 2 is shaped to correspondwith the shape of the upper inner end" of the stress control member andthe inner end of the insulating cone 4. The lower end of the insulatingsleeve extends into the cone 4' andis supported by the cone 4' and thestress control member 5. The lower end of the stress control member issupported on the metallic threaded ring 7 as in Fig. l. A conductor 11connects the conductive member 6 and a closure plate 12 that fits overthe ferrule 8 and seals the lower end of the insulator housing 3.

The assembly of the structures of Figs. 1 or 2 may be carried out in thefollowing manner: The insulating sleeve 2, suitably tapered at its lowerend, is applied to the cable core 1. The support 4 or 4' of the shape ofa truncated cone is then inserted onto the end of the cable core 1, orif the support 4 or 4' is of several parts the portions constituting itare positioned around the bottom of the insulating sleeve 2 and boundtogether. Subsequently, the tube 10 in the case of Fig. 1, or the stresscontrol member 5 in the case of Fig. 2, is positioned on the end of thecable, and the ring 7 is screwed on the ferrule 8. Finally, theinsulating sleeve 2 at its upper end is given the bell-like shape, andthe winding 13 of metallic wire having closely positioned turns isformed around the top of the sleeve 2 to constitute the stress controlscreening of the cable head at its entry into the sealing end. Thescreening wire 13 is grounded to the metallic cable sheath which isgenerally of lead or aluminium. Now the sealing end is ready to receivethe insulator 3 with the rings that are cemented to the upper and lowerends thereof, together with the corresponding upper and lower closingplates that are secured to those rings with interposed gaskets, and theend cap 14, and then be filled with an insulating fluid as, forinstance, oil or an insulating gas. The insulating end may then bepositioned so that the insulator 3 enters through the top of atransformer casing into the transformer housing as is usual in the art.

As previously stated, the sleeve support 4 of Fig. l, or 4' of Fig. 2,may be formed of several prefabricated pieces kept together by means ofa binding of insulating material. This construction is illustrated inFigs. 3 and 4. In this construction there is shown at 24 a truncatedcone which may take the place of the cone 4 of Fig. 1 or the cone 4 ofFig. 2. The truncated cone 24 is made of several prefabricated portions,in this instance three, indicated at 25, 26 and 27, each, in thisinstance, of identical construction and of the same insulating materialas previously described in connection with the cone 4 or 4' of Figs. 1and 2 and made by the method of my application Serial No. 550,741, withor without an internally embedded porous insulating structure acting asa skeleton, as previously referred to. Each portion is, in thisinstance, of the shape of one-third of the ultimate cone. The threeportions 25, 26 and 27 are held together by upper and lower bindings 28and 29 of insulating tape or cord which are wound respectively in uppermating grooves 30 formed in the three cone portions and lowerfunnel-like shape.

The potential of the cable sheath is ground potential or substantiallyground potential, the difference being that sometimes cable sheathsections are isolated to reduce sheath currents and therefore thepotential of the sheath may be a very small number of volts above groundpotential. For the present purposes, this small number of volts isinsignificant in comparison with the potential of the cable conductor,and the cable sheath is therefore considered as being at groundpotential,

While I have here shown and described a few preferred embodiments of myinvention, it is, however, to be understood that the same is merelyillustrative. What I consider new and desire to secure by Letters Patentis:

1. An improvement in the construction of a sealing end for a hightension cable having a cable core, said sealing end having a verticallyextending insulator into which the cable core enters from the top andextends downwardly towards the bottom, characterized in that aninsulating sleeve surrounds the end of the cable core within theinsulator, the lower end of said sleeve being shaped as a generallytruncated cone, and there is provided a support against which theconical surface of the truncated conical end of the sleeve bears, saidsupport being of rigid insulating material of a dielectric strength atleast approximating that of the insulating sleeve and shaped as agenerally truncated cone and into which the lower end of the sleeveextends and by which the conical surface of the sleeve is supportedagainst downward move- 'ment, and means for supporting the supportagainst downward movement.

2. An improvement in the construction of a sealing end for a hightension cable having a cable core impregnated with an insulating fluid,said sealing end having a vertically extending insulator into which thecable core enters from the top and extends downwardly towards thebottom, characterized in that an insulating sleeve surrounds the end ofthe cable core within the insulator, the lower end of said sleeve beingshaped as a generally truncated cone, and there is provided a supportagainst which the conical surface of the truncated conical end of thesleeve bears, said support being of rigid insulating material of adielectric strength at least approximating that of the insulating sleeveand shaped as a generally truncated cone and into which the lower end ofthe sleeve extends and by which the conical surface of the sleeve issupported against downward movement, and means for supporting thesupport against downward movement, said support being perforated toallow the flow of insulating fluid therethrough to and from the cablesleeve.

' 3. An improvement in the construction of sealing ends as in claim 1,characterized in that the support of insulating material is a casting ofsynthetic resins preferably of the ethoxylinic type, with hardeningagents and in case loaded with inorganic excipients.

4. An improvement in the construction of sealing ends as in claim 1,characterized in that the support of insulating material is a porousinsulating structure, acting as a skelton which is impregnated with andembedded in synthetic resins preferably of the ethoxylinic type, addedwith hardening agents but devoid of inorganic fillers.

5. An improvement in the construction of sealing ends as in claim 1,characterized in that the insulating support is made of insulationselected from the group comprising bakelized cardboard, porcelain, andglass.

6. An improvement in the construction of a sealing end assign for a hightension cable through which electrical connections are made with theconductor of the cable core, said sealing end having an outer insulatorinto which the cable core enters at the top and through which it extendsvertically towards the bottom, an outer metal flange terminating thebottom of the outer insulator, characterized in that an insulatingsleeve surrounds the end of the cable core within the insulator andthere is provided a support of rigid insulating material of a dielectricstrength at least approximating that of the insulating sleeve and shapedas a generally truncated cone and into which the lower end of the sleeveextends and by which the sleeve is supported against downward movement,and means for supporting said truncated cone comprising a tube of rigidinsulation surrounding the cable core and upon which the truncated conerests, a ferrule on the end of the cable conductor and means forsupporting the said tube comprising a metal ring screwed on the ferruleand surrounded by the outer metallic flange which terminates the outerinsulator and which serves to screen the end of the terminal and whichis at the same potential as the cable conductor.

7. An improvement in the construction of a sealing end for a hightension cable through which electrical connections are made with theconductor of the cable core, said sealing end having an outer insulatorinto which the cable core enters at the top and through which it extendsvertically towards the bottom, characterized in that an insulatingsleeve surrounds the end of the cable core within the insulator andthere is provided a funnel shaped support of rigid insulating materialof a dielectric strength at least approximating that of the insulatingsleeve and into which the lower end of the sleeve extends and by whichthe sleeve is supported against downward movement, and means forsupporting said support comprising a stress control electrode embeddedin a mass of solid insulation, said electrode surrounding the cablecore, and means for maintaining the electrode at the potential of thecable conductor.

8. A terminator for sealing the end of a high voltage electric cable andestablishing electrical connections with the conductor thereof, saidterminator comprising an outer housing of insulation having upper andlower open ends into one of which the cable conductor extends and at theopposite one of which the cable conductor ends, a sleeve of insulationsurrounding the cable within the housing, an inner hollow truncated coneof rigid insulating material coaxial with the sleeve, the small diameterend of the support being adjacent to the end of the cable core withinthe terminator, and said cone flaring outwardly from the end of thecable conductor towards the end of the terminator into which the cablecore enters, one end of the sleeve extending into the inner cone andbeing supported thereby, and means supporting the small diameter end ofthe inner cone within the outer housing and thereby supporting thesleeve.

9. A terminator for sealing the end of a high voltage electric cable andestablishing electrical connection with the conductor thereof, saidterminator comprising an outer housing of insulation having verticallyaligned upper and lower open ends into one of which the cable coreextends and at the opposite one of which the cable core ends, thehousing being at ground potential at said one end thereof and at thecable conductor potential at the opposite end, a sleeve of insulationsurrounding the cable core within the the housing, an inner hollowtruncated cone of rigid insulating material coaxial with the sleeve, oneend of the sleeve extending into the inner cone and being supportedthereby, and means supporting the smaller diameter end of the inner conewithin the housing and thereby supporting the sleeve, said last meansincluding rigid insulation surrounding the cable core and interposedbetween the smaller diameter end of the inner cone and the parts of theterminator which are at the potential of the cable conductor, thesmaller diameter end of the inner cone being held against verticalmovement by said last mentioned rigid insulation, the housing having afilling of fluid insulation and said inner cone being perforate to allowthe flow of insulating fluid to the insulating sleeve.

10. A terminator for sealing the end of a high voltage electric cableand establishing electrical connections with the conductor thereof, saidterminator comprising an outer housing having upper and lower endsinsulated from each other and into one of which the cable core extendsand at the opposite one of which the cable core ends, a sleeve ofinsulation surrounding the cable core within the housing, an innerhollow truncated cone of rigid insulating material coaxial with thesleeve, the lower end of the sleeve being tapered to the shape of andextending into the inner cone and being supported thereby, and meanssupporting the lower end of the inner cone within the housing, said lastmeans including a tube of rigid insulation surrounding the cable coreand interposed between the smaller diameter end of the inner cone andthe parts of the terminator which are at the potential of the cableconductor and being at its lower end at the potential of the cableconductor, the lower end of the inner cone being held against verticalmovement by said last mentioned tube of rigid insulation.

11. A terminator for sealing the end of a high voltage electric cableand establishing electrical connections with the conductor thereof, saidterminator comprising an outer housing having upper and lower endsinsulated from each other and into one of which the cable core extendsand at the opposite one of which the cable core ends, a sleeve ofinsulation surrounding the cable core within the housing, an innerhollow truncated cone of rigid insulating material coaxial with thesleeve, the lower end of the sleeve being tapered to the shape of andextending into the inner cone and being supported thereby, and meanssupporting the lower end of the inner housing within the outer cone,said last means including a mass of rigid insulation surrounding thecable core and a stress controlling conductive ring embedded in saidmass and electrically connected to parts of the terminator which are atthe potential of the cable conductor, the lower end of the inner conebeing held against vertical movement by said last mentioned rigidinsulation.

12. A stress control member for use with a high voltage cable, saidmember comprising a body of rigid insulation of the shape of a hollowtruncated cone having at its smaller diameter end a sleeve of insulationcoaxial therewith, a stress control conductive ring embedded in thesleeve, a conductive lead extending from the ring to the outside of thesleeve, the insulation of the sleeve being devoid of voids therein andbeing in intimate adherence with the surface of the ring.

13. A stress control member for use with a high voltage cable, saidmember comprising a body of rigid insulation of the shape of a hollowtruncated cone having at its smaller diameter end a sleeve of insulationcoaxial therewith, the cone being perforated to permit the passage ofinsulating fluid through the wall thereof, a stress control conductivering embedded in the sleeve, a conductive lead extending from the ringto the outside of the sleeve, the insulation of the sleeve being devoidof voids therein and being in intimate adherence with the surface of thering.

14. An improvement in the construction of a sealing end for a hightension cable having a cable core, said sealing end having a verticallyextending insulator into which the cable core enters from the top andextends downwardly towards the bottom, characterized in that aninsulating sleeve surrounds the end of the cable core within theinsulator, and there is provided a funnel-shaped support of rigidinsulating material of a dielectric strength at least approximating thatof the insulating sleeve and into which the lower end of the sleeveextends and by which the sleeve is supported against downward movement,said support comprising several prefabricated portions and a binding ofinsulating material holding said portions together and said supportincluding a metallic tubular base for the apex of the funnel which baseis coaxial with the longitudinal axis of the funnel shaped support; andmeans for electrically screening the said tubular base, said last meanscomprising an outer metal flange which terminates the outer insulatorand which is electrically in contact with. the cable conductormaintaining at least a portion of the tubular base at the potential ofthe cableconductor.

15. A structure such as defined in claim 8 wherein the means forsupporting the small diameter end of the inner cone comprises a body ofrigid insulation surrounding the cable conductor and interposed betweenthe lower end of the inner cone and the parts of the terminator whichare at the potential of the lowermost end of the housing, and the saidbody of rigid insulation being, at its lower end, at the potential ofthe housing, the lower end of the inner cone being held against verticalmovement by said last 15 mentioned rigid insulation.

References Cited in the, file of this patent IJNITEI) STATES PATENTSHarris Feb.. 2 3, 1915 Myers Sept. 20, 1932 Hanson Mar. 13, 1934 Bowdenet a1 Sept. 26, 1939 Brazier et a1 July 5, 1949- Nicholas Dec. 20, 1955Roehmann Mar. 18, 1958- FOREIGN PATENTS Great. Britain -Dec. 8, 1937Great Britain Aug. 20, 1940 Australia Pub. June 10, 1954

